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Courtship in birds is often long and complicated, and because of this, it surprised me that many birds don’t stay together after breeding. Birds have different mating systems depending on the species. In this article, we look at the various systems they use.

Birds are either monogamous, staying with a dedicated partner, or polygamous, breeding with more than one partner. There are variations on both of these breeding systems, such as lek polygyny and polyandry, that some species practise.

If you want to know more about the breeding systems of birds, then please read on.

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Monogamy is where the male and female has one dedicated partner, creating a pair-bond. Monogamy is much more common in birds than in mammals, where it is rare. Birds may stay together for part of a season or the whole season, a few seasons, or lasting their entire lives. Most monogamous birds will only remain together for part of a season, with relatively few species staying together forever.

Monogamy does not always have to be for a long time, and some birds practice serial monogamy where they stay with one bird before moving on to another, even in the same breeding season. Because they are only with one bird at a time and help raise the chicks, this is still classed as monogamy, not polygamy.

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Polygamy occurs when the male or female has different mates in the same breeding season. Polygamous birds do not create a pair-bond as monogamous birds do.

There are two types of polygamy, one where the male cheats on the female, called polygyny, and one where the female cheats on the male, called polyandry.

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Polygyny is when one male breeds with many females in one season. The male can have several females impregnated, with eggs in different nests simultaneously. This system is called simultaneous polygyny.

Serial polygyny is when the male contributes towards rearing the chicks and helps incubate the eggs before moving on to another female to breed.

Polygyny is an excellent way to make sure that they reproduce successfully. Males in a resource-rich territory will defend a specific area with plenty of food to ensure the best plumage and song. Females will see this and mate with them. Because the territory has plenty of food, females will see these areas as an excellent place to raise their young.

Areas with the best looking males and plenty of food usually are well protected from predators and the elements. Although the female doesn’t get any help from the males, the territory provides the best start for the chicks in life. Having a plentiful supply of food, lack of predators and low infant mortality rate seem to outweigh the lack of help the female will get from the male.

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Lek Polygyny

Although rare, lek polygyny occurs when there are many males in an area. Females will visit the breeding areas, called leks, and defend a small area where they hold court.

In the courts or arenas, as they are sometimes called, three or four males will make a display for the female, with the most dominant male taking the centre of the arena. Because there are so many males, females can be very selective about who they breed with. Once they have mated, the female will move to a different nesting location.

Many courts are held with different females, and often the same male is chosen repeatedly. Lek polygyny occurs typically when there is no specific resource-rich territory that the males can defend to attract a female.

Birds that hold leks are often more conspicuous than birds that practice monogamy. Their brightly coloured crests, tails, and feathers can bring too much attention to an area generally reserved for monogamous birds and attract predators.

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Much rarer than polygyny in birds, polyandry is when the female has more than one mate. It is thought that less than 5% of all species have polyandrous relationships.

In polyandry species, the female usually is larger and more colourful than the male. Similar to how a male will mark out a resource-rich territory to attract a female, polyandrous females will do the same.

In these cases, incubation and rearing of the chicks is the male’s job while the female protects the territory and finds food. The female is then free to use the energy she would have expended, incubating and rearing her young to lay more clutches of eggs.

If the female may have several nests in one area at the same time, called simultaneous polyandry, the males will help to protect the territory from predators. Serial polyandry is when the female has one nest at a time before moving on to another male.

Polyandry occurs typically in areas where there are many more males than females. Although the male may know that the eggs he is incubating are not his, he needs to ensure that he has a chance to mate. Because males can incubate and raise the young as well as the female, when the female flies off, he has no choice but to raise the young himself for the next generation to survive.

Another reason for polyandry is that in areas where there is a high risk of egg predation, many clutches of eggs can be laid with no further work having to be done by the female.

Why do birds stay with one partner?

Most species of birds are monogamous, with about 90% staying with one partner and forming a pair bond. This is unlike most mammals that practice polygamy. However, the length of time they stay together varies, so the actual figure is probably much lower.

Most birds are monogamous because it gives them the best chance of successfully passing their genes down to their offspring and future generations. This may seem strange as you may think that having as many children as possible would help them pass their genes down, but if their children do not survive, they will not pass their genes on to future generations.

By staying with one partner, even for one season, they can give them the best chance to survive. By rearing their young, they are given the best start in life, and when their offspring are ready to mate, they will be in the best condition and, therefore, pick the best mate.

Polygamous birds generally do not look after their young and not as well as monogamous parents, so although they may have more offspring, the young are not cared for as much, and food and shelter are not as well provided as from a two-parent nest.

Females on their own often struggle to feed all their young. If the young survive, they won’t be in the best condition to find a mate, and their genes will die with them.

Birds, unlike mammals, can look after their young regardless of the sex of the parent. While female mammals need to feed their young milk, female birds don’t. Male birds can find food, feed their young, incubate the eggs, and defend the nest.

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